Thread trimming mechanism for lock stitch sewing machines



March 16, 1965 K. HEDEGAARD 3,173,392

THREAD TRIMMING MECHANISM FOR LOCK STITCH SEWING MACHINES Filed Aug. 7, 1962 2 Sheets-Sheet 1 ILJ .u' I, 4 :i'. IL

24 we II /N mvro/P klrlsrz/v 195775644120 March 16, 1965 K. HEDEGAARD 3,173,392

THREAD TRIMMING' MECHANISM FOR LOCK STITCH SEWING MACHINES Filed Aug. 7, 1962 2 Sheets-Sheet 2 INVENTOR.

rrR/ s 7724/ fl'oetrmw 04 "76% A 7 W R/Vf Y United States Patent Ofitice 3,173,392 THPLEAD TRIMMING MECHANISM FOR LUCK STITCH SEWING MACHINES Kristen Hedegaard, Geutofte, Denmark, assiguor to G. M.

Pfafi A.G., Kaiserslautern, Pfalz, Germany, a corporation of Germany Filed Aug. 7, 1962, Ser. No. 215,317 Claims priority, application Germany, Aug. 11, 1961, P 27,695 Claims. (Cl. 112-252) The present invention relates to thread trimming mechanism for lock stitch sewing machines, more particularly of the type having a cloth or throat plate, a reciprocating needle above said plate and a continuously rotating loop taker below said plate, an important object of the invention being the provision of improved trimming mechanism for severing both the upper or needle thread and the lower or loop taker thread by means of a single operation, said mechanism being designed and operating substantially free from interference with said needle and loop taker and the related stitch forming tools, such as a work feed dog ordinarily disposed between said plate and loop taker, in accordance with conventional lock stitch sewing machine constructions.

There are already known thread trimming devices for the severing of both the loop taker or bobbin thread and the needle thread of a sewing machine by a single operation, wherein the loop taker thread is cut by means of a first cutting knife mounted upon the undersurface of the throat plate and the needle thread is similarly cut by means of a second knife mounted upon the work clamp or presser foot of the sewing machine. Thread trimming devices of this type are quite expensive in construction, inasmuch as separate supporting means and operating mechanisms have to be provided for both the upper and lower thread cutting devices.

There are furthermore known thread trimming devices, wherein the loop taker thread and needle thread are seized by a crescent-shaped catch-thread device mounted upon the undersurface of the throat plate and being moved or operated towards a stationary cutting knife to be cut thereby by cooperation with a cutting edge upon said device. In thread trimming devices of this type, the thread-catch device at first seizes the loop taker thread passing from the bobbin to the work or fabric and thereafter, that is, after the needle has moved outside of the throat plate of the machine, has to seize the needle thread loop formed by the needle, and to feed both threads towards the stationary cutting knife by a swinging movement. During the latter, the thread-catch device passes at a close distance from the take-up limb of the needle thread loop, that is, the limb on the side of the needle or thread take-up lever of the sewing machine, whereby to involve the danger, especially in the case of a relatively narrow loop formed by the needle or in case of relatively high sewing speeds, of cutting the take-up limb of the needle thread loop together with the work limb of said loop, with the result that the length of the cut thread end depending from the needle will be insufiicient for the commencement of a subsequent stitching operation. Furthermore, such thread trimming devices require practically all the available mounting space between the throat plate and the rotary hook or loop taker on account of the thread cutter and stationary cutting knife being mounted upon the undersurface of said plate and on both sides of the stitching hole provided therein. As a consequence, thread trimming devices of this type are practically limited to sewing machines wherein the work feeding means are mounted above the throat plate of the machine, in contrast to the conventional constructions having the feed dog or dogs 3,173,392 Patented Mar. 16, 1965 mounted between the rotary hook or loop taker and said plate.

Accordingly, a more specific object of the invention is the provision of thread trimming mechanism for lock stitch sewing machines having a rotary loop taker and a feed dog both being mounted below the throat plate of the machine, substantially without interfering with the ordinary operation or impeding the accessability of the loop taker and related stitch-forming elements of the machine.

Among the further objects of the invention is the provision of thread trimming mechanism of the type referred to for lock stitch sewing machines by which the loop taker thread and the work limb of the needle thread loop will be cut safely and securely and substantially without the danger of cutting the take-up limb of said loop; which mechanism is both simple in design and compact to enable its mounting in close proximity to the loop taker such as to take up a minimum of mounting space and not to interfere with the conventional construction and operation, as well as accessability, of the stitch-forming tools; and which can be readily adapted for control by the drive or power source of the sewing machine, such as by the operation of a control lever or the like actuating device.

The invention, both as to its ancillary objects as well.

as novel aspects, will be better understood from the following detailed description, taken in conjunction with the accompanying drawings forming part of this specification and in which:

FIG. 1 is an elevational View of a sewing machine equipped with thread trimming mechanism constructed in accordance with the principles of the invention;

FIG. 2 is a more detailed and expanded perspective view of the thread trimming device forming part of FIG. 1 and operably associated with mechanism to operate the same by the driving source of the sewing machine;

FIG. 3 is a partial view of the catch-thread device according to the invention;

FIG. 4 is a perspective View of the loop taker and thread-catch device forming part of the previous figures and being shown in the position of seizing the loop taker thread and work needle thread limb to be cut;

FIG. 5 is a view similar to FIG. 4, showing the threadcatch device in the cutting position; and

FIG. 6 is a partial sectional view taken on line VI-VI of FIG. 2.

Like reference numerals denote like parts and elements throughout the different views of the drawings.

With the foregoing objects in view, the invention involves generally the provision, in connection with a lock stitch sewing machine of the type having a throat plate, a reciprocating needle above said plate, and a cylindrical rotary hook or loop taker having a needle thread seizing beak and being mounted below said plate, of thread trimming mechanism comprising essentially an arcuate catchthread blade conforming and being disposed closely adjacent to the outer surface of and mounted for oscillation coaxially with said loop taker in the direction towards and away from said beak, respectively, in respect to a predetermined starting position relative to said loop taker, to trap and cut the loop taker thread and the work needle thread limb in cooperation with a stationary cutting knife engaging said blade. For the latter purpose, said blade is provided with a point-like projection extending in the direction of the loop taker beak and adapted to deflect the take-up needle thread limb and to enter the space enclosed by said limb, on the one hand, and the loop taker thread and the work limb of the needle thread loop, on the other hand, in the predetermined position of said loop taker upon drawing out the needle thread loop by said beak and prior to the casting off of said loop. This Q9 results in the separation of said loop taker thread and work needle thread limb from the take-up needle thread limb during the first oscillating half-cycle of said blade in the direction towards the loop taker beak. Said blade is furthermore provided with a hook-shaped portion pointing in the direction opposite to said projection and providing a re-entrant recess within and extending in the direction of said projection, whereby to guide and trap the separated loop taker thread and work needle limb within said recess during the second oscillating half-cycle of said blade in the direction away from said beak. During the latter movement, the stationary cutting knife in cooperation with said blade causes a severing of the loop taker thread and work needle thread limb, substantially without affecting the take-up needle thread limb, to thereby leave an adequate projecting length of the needle thread to ensure the safe commencement of a subsequent stitching operation.

In the thread trimming arrangement aforedescribed, a minimum of mounting space is required for the trimming element proper, resulting in the elimination of any interference with the ordinary construction and operation of the stitch-forming tools, that is, the loop taker, feed dogs etc. Moreover, the throat plate remains substantially free of any elements or parts of the trimming mechanism, whereby to enable a ready exchange where different exchangeable types of plates are desirable or required for the performance of different sewing operations.

In thread trimming devices of the type described hereinbefore, special care must be taken to cause both the loop taker thread limb leading to the work or fabric, as well as the limb of the needle thread loop on the side of the work or fabric (work needle thread limb) to be cut close to the work, on the one hand, and to cause the limb of the needle thread loop on the side of the needle or needle thread take-up lever (take-up needle thread limb) to be cut at a sufiicient distance from the needle such as to enable a safe initiation of the next stitching operation. This aim is achieved securely and reliably by the catchthread device of the invention forming a guide and being provided with a re-entrant recess, to both separate and respective threads and to cut the same, in the manner mentioned and further understood as the following detailed description proceeds.

According to a preferred embodiment of the invention, the operation of the thread trapping and cutting device is effected by the driving source of the sewing machine, such as by the provision of releasable coupling means between the loop taker driving shaft and an oscillating disk, lever or the like operating said device through a single oscillation by control of said coupling by means of an operating lever or the like control device. In order to ensure the cutting operation to be coordinated with or carried out at the proper phase or instant of the loop taker rotation, that is, upon drawing out of the needle thread loop and prior to the casting off of said loop, as pointed out hereinbefore, further means, such as a camfollower mechanism inserted in the coupling path between the loop taker shaft and the cutting device, may be pro vided, to disable the coupling except in the aforementioned position of the loop taker. Alternatively, the position of the loop taker for the commencement of the thread trimming operation may be indicated by a pointer or the like cooperaing with one of the stitch-forming elements, such as the needle bar, thread take-up lever etc.

According to still another embodiment of the invention, the sewing machine may be arrested with the needle in its lowermost position, or prior to the loop taker beak seizing the needle thread loop, whereupon the machine drive shaft is operated through a limited or half revolution by the charge previously stored in an electrical capacitor, to cause the loop taker to rotate through a full revolution and to operate the thread cutting mechanism through an oscillating cycle for the cutting of the upper and lower threads in the manner pointed out and described in greater detail in the following in reference to the drawings.

Referring more particuarly to FIG. 1, the numeral 1 represents the bed plate of a conventional sewing machine supporting an upright 2 carrying an overhanging arm 3 which terminates in the sewing head 4. Mounted within the arm 3 is the main drive or arm shaft 5 of the machine being operably connected in a known manner with the reciprocating needle bar 7 carrying a needle 6 and mounted in the head 4. Further secured to the arm shaft 5 is a bevel gear 8 which serves to drive by way of a cooperating bevel gear 9 a vertical shaft 16 mounted within the upright 2. Secured to the lower end of the shaft 10 is a further bevel gear 11 meshing with a bevel gear 12 driving the loop taker shaft 13 mounted below the bed 1 and carrying a rotary hook or loop taker 14 at its opposite end, in a manner well known and understood.

Adjustably mounted by means of a pair of set screws 17 upon the arc-shaped carrier 15, FIG. 2, conforming to the outline of and disposed in closely spaced relation to and coaxially with the loop taker 14 is an arcuate catch-thread device or blade 16. The latter, thus being disposed between the outer cylindrical surface of the loop taker 14 and feed dog 18, is provided with a lateral point-like projection 20, FIG. 3, pointing in the direction of the needle thread seizing beak 19 of the loop taker 14. Blade 16 is furthermore provided laterally of the arrow-shaped point 20 with a thread trapping hcok-shaped portion 21 pointing in the opposite direction and being, in turn, provided with a re-entrant recess 23 within and extending in the direction of the point 26. Secured to the undersurface of the bed 1, as shown in dotted lines in FIG. 2, is a cutting knife 24 engaging the point 20 of the catch-thread device 16 for cooperation therewith in trimming the loop taker and needle threads, in the manner described in further detail in the following.

Extending transversely from the carrier 15, being coaxial with the loop taker shaft 13, is a connecting bar or arm 25 secured to a rotating or oscillatable ring or disk 26. The disk 26 also mounted coaxially with and encircling the shaft 13 is journalled in a ring 28 mounted upon the bed or base 1. Axial displacement of the disk 26 is prevented by the provision of a segmental ring or cover 29 secured to the side of the ring 2%. Disk 26 has a projecting pin 30 to which is pivoted one end of a link or connecting rod 31 the opposite end of which is, in turn, linked to a pin carried by a crank disk 33 mounted upon an auxiliary shaft 34 being parallel to the loop taker drive shaft 13 and also mounted below the bed 1.

Loosely mounted upon the auxiliary shaft 34 is a gear 35 being in driving connection with a gear 38 mounted upon the loop taker shaft 13 through an intermediate gear 36 having a shaft 37 mounted upon the bed 1. Further connected to the shaft 34 is a cupshaped coupling disk 39 carrying a pin 40 rotatably supporting one end of an arcuate follower arm 41 which has its opposite hook-shaped end arranged to embrace a pin 43 projecting laterally from the gear 35, the angularly bent opposite end 44 of said follower 41 engaging a recess 45 in the coupling disk 39 and being urged towards the upper wall 47 of said recess by a spring 45.

Furthermore rotatably mounted within the arm 3 is a bolt 48, FIG. 1, carrying a first lever 49 arranged to cooperate with the thread tension release of the sewing machine, to release the tension of the needle thread upon rotation of the bolt 48. The latter being fitted with a second control lever 50' is connected through a link 51 with one end of a horizontal draw rod 52 the opposite end of which is linked to one arm 53 of a bellcrank lever 54 fulcrumed within the arm 3. The remaining arm 55 of the bellcrank lever 54 is, in turn, linked to a vertical dr-aw rod 56 having its lower end connected to a cont-r01 rod 58 through a universal or ball joint 57. Control rod 53 is secured to a one-arm lever 59 rotatably supported by a shaft 61 mounted upon the bed 1 and being fitted with a biasing spring 60 to urge the lever 59 to rotate in counterclockwise direction. The free end of lever 59 carries a pin 62 normally urged to a position of disengagement from a cam disk 63 mounted upon the loop taker shaft 13 by the action of the spring 60. Connected to the front end of the shaft 61 is a further lever 64 carrying a pin 65 which engages the underside of a release lever 66. The latter being connected at one end to a bolt 67 journalled in the bed 1 has its opposite end fitted with a pawl 66 which in the rest position of the thread trimming device is locked between the end 44 of the follower 41 and the upper limit surface or abutment 47 of the recess 45 of the coupling disk 39. In order to ensure a safe locking of the pawl 68, the release lever 66 is continuously urged against the outer surface 70 of the disk 39 by the action of a coil spring 69 encircling the bolt 67, disk 39 being furthermore formed with a bevelled surface 71 to facilitate locking engagement of the pawl 66.

The recess 45 of the coupling disk is shaped with a stepped contour, in such manner that the pawl 6% of the release lever 66 having a lateral projection '72 is enabled to engage or lock within the space between the upper surface 47 of the recess 45 and the end of the follower 41, while preventing a locking of the pawl 66 between the end of the follower 41 and the lower limit surface or abutment '73 of the recess 45 by the projection '72 engaging the outer surface of the disk 39.

The operation of the thread trimming mechanism aforedescribed is as follows.

At the endof a sewing operation with the needle 6 being in its lowermost position, the control lever 51?: is operated to the left, whereby, in addition to the release of the upper thread tension, the draw rod 52 is also displaced towards the left by the link 51. As a consequence, the bellcrank lever 54 lifts the draw bar 56 which, in turn, imparts a swinging movement to the lever 59.

The purpose of the cam disk 63 mounted upon the loop taker shaft 13 is to define the commencement of the thread trimming operation, inasmuch as a swinging movement of the lever 59 will be possible only if the pin 62, normally being urged away from the cam surface by the spring 66, engages the lowest or innermost point of said surface. In this position of the cam 63, the loop taker beak 19 is positioned exactly in the middle of the needle thread loop.

The lever 59 transmits its swinging movement to the lever 64, causing, in turn, a lifting of the release lever 66 by the pin 65. As a consequence, the pawl 68 is disengaged from the recess 45, whereby to cause the end 44 of the follower 41 to engage the upper abutment surface 47 of said recess by the action of the spring 46. This, in turn, causes the follower 41 to rotate about its pin or pivot 46, whereby to project its hook-shaped end 42 into the path of the pin 43, in such a manner as to partly embrace or engage the latter. As a consequence, rotary motion transmitted from the loop taker shaft 13 to the gear 35 will be imparted to the coupling disk 39 and auxiliary shaft 34 by way of the follower 41 and pin 41). The rotary motion of the shaft 34 is converted into oscillatory motion of the disk 26 and connecting rod 25 by way of the crank disk 33 and link 31. As a result, the arrow point 2% of the threadcatch device 16 begins its first half-cycle oscillation in the direction of the loop taker beak 19, after said beak has seized and enlarged the needle thread loop. During this oscillating half-cycle, the point 24 of the blade 16 enters across the path of the needle 6 (FIG. 4) the loop formed by the needle thread, in such a manner that the limb of said loop leading to the needle or thread take-up lever will be deflected towards the right by the 6 right edge '74 of the point 21 (FIG. 3), while the limb of said loop adjacent to the work or fabric, together with the loop taker or bobbin thread also leading to the work, slides along the left edge '75 of the point 20 such as to be seized by the hook 21. After the needle thread loop seized by the beak 19 and carried over the bobbin thread casing has been cast off from the latter, the catch-thread blade 16 starts its second oscillation half-cycle or return movement, during which the takeup needle thread limb and the loop taker thread linb leading to the work will be returned along the undersurface of the point 29, or between the blade 16 and the loop taker 14, by the hook 121, while the work needle thread limb and limb of the loop taker thread adjacent to the work will be trapped within the recess 23 extending in the direction of the point 20. During the return movement or half-cycle oscillation of the blade 16 (FIG. 4), the hook 21 acts to draw a corresponding length of both the needle and loop taker threads from the needle thread and loop t-aker thread bobbins, respectively. Furthermore, the work needle thread and work loop taker thread limbs trapped by the recess 23 are fed by the hook 21 to the stationary cutting knife 24 (FIG. 4) mounted upon the bed 1 and engaging the blade 16, whereby to sever the threads upon engagement of the inner edge of said recess by the edge of the knife 24.

During the rotation of the loop taker shaft 13 the pawl 63 engages the surface 70 of the coupling disk 39 by the action of the spring 69. Shortly after the termination of a full revolution, the pawl slides along the beveled surface portion '71, whereby to push back the end 44 of the follower 41 against the action of the spring 46, until the space between the upper abutment 47 of the recess 45 and the end 44 of the follower 4-1 has become sufficient to enable said pawl to engage the recess 45. As a consequence, the follower 41 is again deflected about the pin 40 such as to cause its free end 42 to be moved out of the path of the pin 43, thereby to interrupt the driving connection between the shafts 1.5 and 34.

According to an alternative embodiment of operating the thread trimming mechanism, the sewing machine may again be stopped with the needle in the lowermost position, preferably by the provision of known automatic stop motion means to arrest the operation of the machine at this position of the needle. Suitable further means are provided to cause the machine or the arm shafts to perform one half revolution, resulting in a full revolution of the loop taker shaft 13, auxiliary shaft 34, and operation of the catch-thread device 16, to cut the loop taker and needle threads in the manner described herein. An arrangement of this type is included, by way of example, in FIG. 1, wherein the lever arm 59 carries a first electrical contact 3% disposed opposite a cooperating stationary contact 81, said contacts being connected to an electrical capacitor 85 arranged for connection to the power source 83 of the motor 82 driving the sewing machine upon closing of the double-pole operating switch 84, whereby to charge the capacitor to the voltage of said source. After disconnection of the motor 82, to stop the machine, by the opening of the switch 34, as shown in the drawing, the capacitor 85 will be connected to the motor 82 by the actuation of the lever 59 by the control lever 56, in the manner described. As a consequence, the contacts and 81 will be closed, thus starting and operating the motor 82 during one half revolution, provided a proper design of the electrical capacitance of the capacitor 85 for a given operating voltage of the source 83, as will be readily understood.

In the foregoing the invention has been described with reference to a specific illustrative device. It will be evident, however, that variations and modifications, as well as the substitution of equivalent parts and elements for those shown herein, may be made without departing from the broader scope and spirit of the invention, as set forth in the appended claims. The specification and drawings are accordingly to be regarded in an illustrative rather than in a restrictive sense.

I claim:

1. In combination with a lock stitch sewing machine having a throat plate, a reciprocating needle above said plate, and a cylindrical rotating loop taker having a needle thread seizing beak and mounted below said plate, thread trimming mechanism comprising an arcuate blade conforming and disposed in close proximity to the outer surface of and mounted for oscillation concentrically with said loop taker, said blade having a point-like projection in the direction of rotation of said beak adapted to enter the space enclosed by the loop taker thread and the work limb of the needle thread loop, on the one hand, and the take-up limb of said loop, on the other hand, in the predetermined position of said loop taker upon drawing out of the needle thread loop by said beak, whereby to separate the loop taker thread and work needle thread limb from the take-up needle thread limb during the first half-wave oscillating movement of said blade in the direction of said beak, said blade further having a lateral hook-shaped portion in the direction opposite to said projection providing a re-entrant recess within and extending in the direction of said projection, to guide and trap the separated loop taker thread and work needle thread limb within said recess during the second half-wave oscillating movement of said blade in the direction opposite to said beak, operating means to effect a complete oscillating movement of said blade, and a stationary cutting knife engaging said biade at the end of said second movement, to sever loo-p taker and needle threads trapped within said recess.

2. In thread trimming mechanism for sewing machines as claimed in claim 1, a main drive shaft operably connected with said needle, an auxiliary drive shaft driving said loop taker and coupled with said main drive shaft, said operating means comprising releasable intermittent coupling means between said auxiliary shaft and said blade and including means to actuate the same in said predetermined loop taker position, to operate said blade through a complete reciprocating cycle, to trap and out said needle and loop taker threads.

3. In thread trimming mechanism for sewing machines as claimed in claim 1, a main drive shaft operably connected with said needle, a first auxiliary shaft driving said loop taker and coupled with said main shaft, said operating means comprising an oscillating disk coaxial with said loop taker and connected to said blade, a second auxiliary shaft, coupling means between said second auxiliary shaft and said disk, to convert rotary motion of said second auxiliary shaft into oscillating motion of said disk, to reciprocate said blade, and releasable cou pling means between said first and second auxiliary shafts including means to actuate the same in said predetermined loop taker position.

4. In thread trimming mechanism for sewing machines as claimed in claim 1, a main drive shaft operably connected with said needle, a first auxiliary shaft driving said loop taker and coupled with said main shaft, said operating means comprising a rotating disk coaxial with said loop taker and connected to said blade, a second auxiliary drive shaft, coupling means between said second auxiliary shaft and said disk, to convert rotary movement of said second auxiliary shaft into oscillating movement of said disk, to reciprocate said blade, and releasable coupling means between said first and second auxiliary shafts and including means to actuate the same in said predetermined loop taker position, to intermittently operate said second auxiliary shaft through a single rotation.

5. In thread trimming mechanism for sewing machines as claimed in claim 4, said last means comprising a cam 8 and follower connection between said releasable coupling neans and said first auxiliary shaft, to normally disable said coupling means except in said predetermined loop taker position.

6. In thread trimming mechanism for sewing machines as claimed in claim 1, a main drive shaft operably connected with said needle, a first auxiliary drive shaft for said loop taker coupled with said main drive shaft, said operating means comprising a first rotating disk coaxial with said loop taker and connected with said blade, a second auxiliary shaft carrying a second disk, a link connecting said disks to convert rotation of said second auxiliary shaft into oscillating movement of said first disk, to reciprocate said blade, releasable coupling means between said first and second auxiliary shafts, and means to intermittently rotate said first auxiliary drive shaft through a single revolution upon actuation of said releasable coupling means, said last means comprising an electrical capacitor charged during the operation of the sewing machine and connectable to said machine responsive to the operation of said coupling means after disconnection of the machine from its main power source.

7. In combination with a lock stitch sewing machine having a throat plate, a reciprocating needle above said plate, a cylindrical rotating loop taker having a needle thread seizing beak and mounted below said plate, and a feed dog intermediate said plate and said loop taker, thread trimming mechanism comprising an arcuate blade conforming to and being disposed in closely spaced relation to the outer surface of said loop taker, an oscillating driving disk coaxial with said loop taker and means connecting the same with said blade, to oscillate said blade coaxially with said loop taker, said blade having a point-like projection in the direction of rotation of said beak and adapted to enter the space enclosed by the loop taker thread and the work limb of the needle thread loop, on the one hand, and the take-up limb of said loop, on the other hand, in the predetermined position of said loop taker upon drawing out the needle thread loop by said beak, whereby to separate the loop taker thread and work needle thread limb from the take-up needle thread limb during a first half-wave oscillating movement of said blade in the direction of said beak in said predetermined position of said loop taker, said blade further having a lateral hook-shaped portion opposite to said projection and providing a re-entrant recess within and extending in the direction of said projection, to guide and trap the separated loop taker and needle threads within said recess by a second half-wave oscillating movement of said blade in a direction opposite to said beak, operating means to impart a single intermittent oscillating movement to said disk, and a stationary cutting knife in predetermined relation to said blade, to sever the trapped loop taker and needle threads at the end of said second movement of said blade.

8. In combination with a lock stitch sewing machine having a throat plate, a reciprocating needle above said plate, and a cup-shaped rotary loop taker having a driving shaft and a needle thread seizing beak and mounted below said plate, thread trimming mechanism comprising an arcuate catch-thread blade conforming to and disposed closely to the outer surface of said loop taker, an oscillating driving disk mounted coaxially with said loop taker and encircling said shaft, means connecting said disk with said blade, said blade having a point-like projection in the direction of rotation of said beak adapted to deflect the take-up limb of the needle thread loop and to enter the space enclosed by said limb, on the one hand, and the loop taker thread and the work limb of said loop, on the other hand, in the predetermined position of said loop taker upon drawing out of the needle thread loop, whereby to separate the loop taker thread and work needle thread limb from the take-up needle thread limb by a first halfcycle oscillating movement of said blade in the direction of said beak in said predetermined loop taker position,

said blade further having a lateral hook-shaped portion forming a re-entrant recess within and in the direction of said projection, to guide and trap the separated loop taker and needle threads within said recess by a second halt-cycle oscillating movement of said blade in a direction opposite to said beak, means to impart a full oscillating movement to said blade in said predetermined looper position, and stationary knife means engaging said blade, to cut the trapped loop taker and needle threads at the end of said second movement of said blade.

9. In thread trimming mechanism for sewing machines as claimed in claim 8, a main drive shaft operably connected to said needle, an auxiliary drive shaft driving said loop taker and coupled with said main drive shaft, said operating means comprising releasable coupling means between said auxiliary shaft and said disk and actuating means therefor, to impart a single intermittent oscillating movement to said disk in said predetermined loop taker position.

10. In combination with a lock stitch sewing machine having a throat plate, a reciprocating needle above said plate, and a rotary loop taker having a needle thread seizing beak and mounted below said plate, thread trimming mechanism comprising an arcuate blade conforming to and being disposed closely adjacent to the outer surface of said loop taker, means responsive to the position of said loop taker to reciprocate said blade through a single oscillation coaxially and in synchronism with a full revolution of said loop taker in respect to a starting position relative to said loop taker upon drawing out the needle thread loop by said beak, said blade having a point-like projection in the direction of rotation of said beak adapted to deflect the take-up limb of said loop and to separate the loop taker thread and work limb of said loop from said take-up limb during the first half-cycle oscillating movement of said blade in the direction of said beak, said blade further having a hook-shaped portion forming a re-entrant recess within and in the direction of said projection, to guide and trap the separated loop taker thread and work needle thread limb Within said recess during the second half-cycle oscillating movement of said blade in the direction opposite to said beak, and stationary cutting knife means engaging said blade, to cut the trapped loop taker and needle threads at the end of said second movement of said blade.

References Cited by the Examiner UNITED STATES PATENTS 1,401,973 1/22 Fifield 112--252 1,820,569 8/31 Kiewicz 112-252 1,883,654 10/32 Ericsson 112252 2,044,754 6/36 Lawrence 19228 XR 2,3 76,417 5/45 Chudner 112252 2,858,786 11/58 Benink et al 112252 OTHER REFERENCES IBM Technical Disclosure Bulletin, Positive Dog Clutch by R. E. Schopp, vol. 1, No. 4, December 1958, p. 12.

JORDAN FRANKLIN, Primary Examiner.

THOMAS J. HICKEY, Examiner. 

1. IN COMBINATION WITH A LOCK STITCH SEWING MACHINE HAVING A THROAT PLATE, A RECIPROCATING NEEDLE ABOVE SAID PLATE, AND A CYLINDERICAL ROTATING LOOP TAKER HAVING A NEEDLE THREAD SEIZING BEAK AND MOUNTED BELOW SAID PLATE, THREAD TRIMMING MECHANISM COMPRISING AN ARCUATE BLADE CONFORMING AND DISPOSED IN CLOSE PROXIMITY TO THE OUTER SURFACE OF AND MOUNTED FOR OSCILLATION CONCENTRICALLY WITH SAID LOOP TAKER, SAID BLADE HAVING A POINT-LIKE PROJECTION IN THE DIRECTION OF ROTATION OF SAID BEAK ADAPTED TO ENTER THE SPACE ENCLOSED BY THE LOOP TAKER THREAD AND THE WORK LIMB OF THE NEEDLE THREAD LOOP, ON THE ONE HAND, AND THE TAKE-UP LIMB OF SAID LOOP, ON THE OTHER HAND, IN A PREDETERMINED POSITION OF SAID LOOP TAKER UPON DRAWING OUT OF THE NEEDLE THREAD LOOP BY SAID BEAK, WHEREBY TO SEPARATE THE LOOP TAKER THREAD AND WORK NEEDLE THREAD LIMB FROM THE TAKE-UP NEEDLE THREAD LIMB DURING THE FIRST HALF-WAVE OSCILLATING MOVEMENT OF SAID BLADE IN THE DIRECTION OF SAID BEAK, AND BLADE FURTHER HAVING A LATERAL HOOK-SHAPED PORTION IN THE DIRECTION OPPOSITE TO SAID PROJECTION PROVIDING A RE-ENTRANT RECESS WITHIN AND EXTENDING IN THE DIRECTION OF SAID PROJECTION, TO GUIDE AND TRAP THE SEPARATED LOOP TAKER THREAD AND WORK NEEDLE THREAD LIMB WITHIN SAID RECESS DURING THE SECOND HALF-WAVE OSCILLATING MOVEMENT OF SAID BLADE IN THE DIRECTION OPPOSITE TO SAID BEAK, OPERATING MEANS TO EFFECT A COMPLETE OSCILLATING MOVEMENT OF SAID BLADE, AND A STATIONARY CUTTING KNIFE ENGAGING SAID BLADE AT THE END OF SAID SECOND MOVEMENT, TO SEVER THE LOOP TAKER AND NEEDLE THREADS TRAPPED WITHIN SAID RECESS. 